imap.comcast.net server not responding

Up until Saturday, 9/1, I was receiving mail from Comcast on my iPhone and iPad. I checked my settings and they are correct. Chatted with a tech rep but the problem is not resolved. When trying to receive email, I get a message "imap.comcast.net server is not responding check your settings. I also lost my inbox and several folders. Is anyone else having this problem?

Re: imap.comcast.net server not responding

Found solution in another thread ... will copy-n-paste.

BOTTOM LINE: I changed server from ...

imap.comcast.net

to ...

imap.ge.xfinity.com

=========SOLUTION=============

In a nutshell, I think even though portions of the auto configuration (some server settings and smtp) where acquired, the imap server address was actually being resolved with IPv6 somehow prioritized over IPv4(?). Upon modifying the /etc/default/grub file is described in this discussion:https://askubuntu.com/questions/1046057/disabling-ipv6-in-ubuntu-18-04, I was able to block IPv6 and its name resoluntion. Once I did this, updated grub and rebooted, ifconfig no longer displayed a dynamically assigned IPv6 address. I then opened Thunderbired, modified the IMAP account settings, entering Comcast's published imap.comcast.net server address and guess what? It worked.

In summary... If you're using IPv6 and trying to connect to imap.comcast.net and experiencing connection problems, you can either disable IPv6 use "imap.comcast.net" or change the server address to "imap.ge-xfinity.com". Not certain, but Thunderbird appears to beprioritizing IPv6 name resolution is prioritized over IPv4. In addition, Comcast doesn't appear to be aware of this and hasn't published the imap.ge-xfinity.com server address. Something has changed there at comcast and not every network admin/engineer may be aware; because the IPv4 & IPv6 host names and addresses are not synched to the host(s). It took an Ubuntu bug and the orginal post in this thread for me to derive this. ugh!

Re: imap.comcast.net server not responding

For a few weeks we have had a similar email download problem, with the Comcast imap server having devolved from instant response to one taking about 25 sec each time it was polled. I too thought that this was a Comcast problem, but it turns out that the fault is with Mozilla Thunderbird.

Within the last few weeks, Thunderbird on both computers has been upgraded to version 60.3.2, in which the default connection protocol was secretly "upgraded" from IPv4 to IPv6, which the Comcast imap server does not recognize. As a result, Thunderbird tries and tries to make the connection with IPv6, sometimes taking over 25 seconds, before dropping down to v4, and picking up the email. The details of the problem are discussed here:

Of the several solutions offered, I chose the simplest, namely disabling IPv6 on Thunderbird, thereby forcing the connection to IPv4, and restoring my client to an instant connection with imap.comcast.net. If you use the Thunderbird client with several servers, you might choose to try the second method, just forcing theIPv4 use on specific server, and not on others.

Here's how: in Thunderbird, goto Tools>Options. On the Options screen, select "advanced" tab > "General" subtab, and in the lower right corner find the button "Config Editor" Click on it, acknowledge the warning, and scroll a long ways down to:

network.dns.disableIPv6 boolean (default: false) Double-clikc on the line, and the value will change to "true" Back out and Okay, shut down and restart Thunderbird, and your client will connect to the imap server in a flash.

This concept may be applicable to other clients, and likely with Cocast's POP server as well.

Re: imap.comcast.net server not responding

In point of fact, at the time the delay problem appeared, I was still using the Comcast POP server, and I switched to IMAP at Comcast's recommendation, only to have the same problem, which turns out to have been initiated by the upgrade of my Thunderbird to v60.3 .

If you don't have this delay, you may still be using an earlier version of Thunderbird, in whihc case, don't do the v60 update.